Radio receiving circuits



Aug. 11, 1931-. M. M. PHILLIPS 3,

RADIO RECEIVING CIRCUITS Filed April 17, 1 929 Tbiasing voltage on the grid.

Patented Aug. 11, 1931 MAURICE rnrnnrrs, or rrrrszsunen, nnnnsyaamnm "R D R EI I G aG R lfl application filed .April 17,

"This invention relates to the art .of radio signalling and is for a receivingcircuit for use in radio communication. The invention constitutes. an improvementon the invention disclosed in my prior Patent No. 1,674,-

"448, and myapplicationfieria'l No."319,80'6,

Tfiled. November 16, I928.

The present invention .is particular'ly applica'ble to receivingcircuits wherein a balancing' circuit is used in the grid circuit of the detectorjtube in place of the usual devices for efiecting rectification, as for instance, a grid leak and grid condenser .01 a

In my said 'applicationSerial N 0. "319,806, I have disclosed a neutralized oscillator de- "tector wherein detection is effected without resorting to .the .useof .a grid leak or a grid condenser, or any of the other means commonly resorted to in causing a three-element tube to function as a detector. In the said application, I have also disclosed a stage of tuned radio frequency amplification disposed in advance of the oscillator detector with a common means for tuning both the amplifying circuit and the detecting circuit, provision being made for impressing the output of the amplifying circuit on the grid of the oscillating detector tube.

Such a system as disclosed in my said application secured the sensitivity of a tuned radio frequency amplification circuit with the highly selective properties of a heterodyne circuit, while rendering the operation of the circuit less critical.

According to the present invention, I have .1929. Serial No.,3f5,5,949.

,larly high sensitivity is secured where ith'e platevoltage on theoscillator detector is in "the vicinity of "fifteen vol'ts, voltages much higher than :this having heretoforefbeen emplo ed. p p v lie-invention maybe readily understood by .referencefto the accompanying drawings, which shows diagrammatically receiving circuit embodying my invention, gthe figure being aconventi'ona'l diagram.

In the drawing, 2 ,designatesa three-ele- 'ment electron 'tube which maybe either :the direct current :or alternating current type, the tube "having a cathode3, axgfid '4 and a plate .5. j i

At 6 is an inductance, which is preferably in the formof a toroidal coiL. One endof the .coil'fi is directly connected with-the grid through a wire 7.. Connected across the twoends of the;coil is a tuning condenser 8. Shunted around the condenser Sis a bridge circuit containing a variablecapadity "9 and afixed capacity '10. v V

Tapped into the midpoint of :Ethe coilG is a lead wire 11 which .connects with an 'l l Bridged around the'inductance 6is a wire 13having one end connected to the lead 11 and having its other end connected "to ,the -cathode circuit at 1.4L "the"bridge circuit 13 including a {radio frequency choke 15. The

provision 'of a radio frequency choke .oif "some type in the bridge circuit "13 appears to be quite important to the successful 'operation of the circuit. g l 1 "Connected with "theplate 5 is a wire 17 flea-dingto a feed back inductance 1'8 induo tively disposed'ad'j'acent one side of the neutralized .coil ,6.'}The other end of the feed back coil 18 connects through a wire .1-19 and the primary windingeopf a, radio frequency transformer to the positive side of a sourceof plate voltage '21. "Theothjer side of the source of plate voltage is con.

f r W din qifi e b b g d "by a by pass condenser=23- inthe customaryfashaadfa t'yfpass ma e iaeaaayaaga .95 "nectetl to the cathode of the tube through i I Tearwi-re 22'intthe usual manner. Theitranscommercial provided around the source of plate current voltage 21.

In the operation of the circuit, the source of plate voltage 21 is preferably about fifteen volts, the greatest sensitivity and se lectivity being obtained with this as the approximate maximum voltage. WVhere the plate voltage is considerably in excess of fifteen, I have found that the circuit is less selective and tunes more broadly. The variable capacity 9 is adjusted according to the characteristics of the circuit to secure neutralization. The circuit is operated through the tuning condenser 8, the tuning being much the same as that of any ordinary superheterodyne circuit.

By the use of the counterpoise or aerial 12 connected to the midpoint of the inductance 6, and by the provision of the bridge circuit 13 including the radio frequency choke coil 15, the circuit is much more sensitive than the usual heterodyne circuit and at the same time is just as selective. Furthermore, it is very stable and easy to con trol, so that it can be satisfactorily used in radio receiving sets, where highly critical characteristics are objectionable. Much of the desirable characteristics of the circuit disclosed in my said patent and the improvement thereon disclosed in my said application is retained in the present circuit with the elimination of the stage of tuned radio frequency amplification with the consequent elimination of parts and the simplification of the circuit. The apparatus following the primary winding 20 of the transformer in the plate circuit may be of any preferred or conventional apparatus.

WVhile I have illustrated and described a preferred embodiment of the invention, it

tor detector tube having a cathode, a grid and a plate, a neutralized inductance in the grid circuit of the tube, an antenna connected to the midpoint of said inductance, and a shunt circuit connecting the midpoint of the inductance and the cathode of the tube and having a radio frequency choke therein.

2. In a radio receiving circuit, an 0scillator detector circuit including a tube having a cathode, a grid and a plate, means for i neutralizing the oscillating detector circuit against self-oscillation comprising a grid circuit having inductance arms and capacity arms and further characterized by the fact that said neutralizing means takes the place of a grid leak and grid condenser, a signal input lead wire connected to a point in the bridge circuit, and a shunt circuit around the neutralized detector circuit connecting the input lead and the cathode of the de tector tube and having a radio frequency choke therein.

3. In a radio receiving circuit, an oscillator detector circuit including a tube having a grid, cathode and a plate, means including an inductance in the grid circuit for neutralizing the oscillator detector circuit against self-oscillation, an aerial connection at the midpoint of the inductance, and a shunt circuit from the aerial connection to the cathode of the tube having a radio frequency choke therein.

4. In a radio receiving circuit, an oscillator detector circuit including a tube having a grid, cathode and a plate, means including an inductance in the grid circuit for neutralizing the oscillator detector circuit against self-oscillation, an aerial connection at the midpoint of the inductance, and a shunt circuit from the aerial connection to the cathode of the tube having a radio frequency choke therein, said neutralizing means serving also in the place of a rid capacity for the tube.

11 testimony whereof I have hereunto set my hand.

MAURICE M. PHILLIPS. 

